Chapter 17: Problem 19

What is the difference between permafrost and ground ice?

Short Answer

Expert verified

Permafrost is permanently frozen ground, regardless of its composition, while ground ice specifically refers to the ice contained within the permafrost.

Step by step solution

Definition of Permafrost

Permafrost is a type of ground - soil or rock, which remains at or below the freezing point of water for two or more years. It doesn't necessarily contain water but describes a state of chronic coldness.

Definition of Ground Ice

Ground ice, on the other hand, refers explicitly to water in the form of ice present within permafrost. This could be in many forms, such as ice wedges, ice lenses, segregated ice, etc.

Highlighting the Difference

The main difference between the two lies in their composition. While permafrost is not required to contain ice, just a state of chronic coldness, ground ice must contain water frozen into ice. This means that all ground ice is in permafrost, but not all permafrost contains ground ice.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Definition of Permafrost

Permafrost refers to the layer of soil or rock that has remained at or below 0°C (32°F) for at least two consecutive years. It's a thermal condition, and the term 'perma' suggests the permanence of the low temperatures that characterize this part of the Earth's surface. Importantly, permafrost does not imply the presence of ice; instead, it is a measure of chronic coldness in the soil.

Definition of Ground Ice

Ground ice is water that has frozen within the soil and is located in the permafrost layer. Unlike permafrost, which is defined by temperature, ground ice is specifically about the material—frozen water within the soil matrix. It can take various forms, including but not limited to, ice wedges, ice lenses, and segregated ice. Ground ice contributes to the volume of the permafrost layer but requires specific conditions to form and persist.

Composition of Permafrost

Permafrost consists of a combination of soil, rock, organic materials like plant residue, and occasionally, ice. The presence of ice within permafrost can significantly impact its physical properties, such as strength and stability. When permafrost contains a high volume of ground ice, it can be particularly sensitive to temperature changes. This can lead to thawing and potential ground subsidence, posing challenges for infrastructure in cold regions.

Chronic Coldness in Soil

Chronic coldness in soil, which defines permafrost, results from the soil temperature being below freezing for extended periods. It's not a temporary frost event but rather a persistently cold condition that affects soil dynamics, biological activity, and the soil's ability to store carbon. This prolonged cold state is critical for maintaining the permafrost and, by extension, the landscapes and ecosystems that rely on it.

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What is the difference between permafrost and ground ice?

Short Answer

Step by step solution

Definition of Permafrost

Definition of Ground Ice

Highlighting the Difference

Key Concepts

Definition of Permafrost

Definition of Ground Ice

Composition of Permafrost

Chronic Coldness in Soil

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